// Numbas version: finer_feedback_settings {"name": "Exact values for sin, cos, tan (0 to 2pi, radians)", "extensions": ["geogebra"], "custom_part_types": [], "resources": [["question-resources/unit_circle_working_radians.svg", "unit_circle_working_radians.svg"], ["question-resources/exact_values_radians.svg", "exact_values_radians_1THxMnw.svg"], ["question-resources/ASTCwhite.png", "ASTCwhite_4z47Ylp.png"]], "navigation": {"allowregen": true, "showfrontpage": false, "preventleave": false, "typeendtoleave": false}, "question_groups": [{"pickingStrategy": "all-ordered", "questions": [{"name": "Exact values for sin, cos, tan (0 to 2pi, radians)", "tags": [], "metadata": {"description": "
testing sin, cos, tan of random(0,90,120,135,150,180,210,225,240,270,300,315,330) degrees but in radians
", "licence": "Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International"}, "statement": "Often we prefer to work with exact values rather than approximations from a calculator. In this question we require you input your answer without decimals and without entering the words sin, cos or tan. For example, to input the exact value of $\\sin\\left(\\dfrac{\\pi}{3}\\right)$, which is $\\dfrac{\\sqrt{3}}{2}$, you would input sqrt(3)/2
", "advice": "Recall the unit circle definitions:
\nIn particular, the angle of $\\var{thetadisplay}$ puts the point {textquadrant}.
\n{diagram}
Since this point falls on an axis and the point is on the unit circle, it is clear that its coordinates are $(\\var{cos({thetarad})}, \\var{sin({thetarad})})$. From these, we can conclude that
\n$\\sin\\left(\\var{thetadisplay}\\right)=\\var{sin({thetarad})}$,
\n$\\cos\\left(\\var{thetadisplay}\\right)=\\var{cos({thetarad})}$, and
\n$\\tan\\left(\\var{thetadisplay}\\right)=\\dfrac{\\sin\\left(\\var{thetadisplay}\\right)}{\\cos\\left(\\var{thetadisplay}\\right)}=\\dfrac{\\var{sin({thetarad})}}{\\var{cos({thetarad})}}\\var{if(theta=90 or theta=270, \" which is undefined\",\" = \" + precround(tan(thetarad),0))}.$
\nThe triangle {textquadrant} has the same side lengths as the related triangle in the first quadrant (they are congruent). Therefore, we can recall or use right-angled triangle trigonometry to determine the lengths of the triangle in the first quadrant and then change the signs as needed. Recall:
\nBy drawing the following triangles, we can determine the exact values of $\\sin$, $\\cos$ and $\\tan$ for the angles $\\dfrac{\\pi}{6}$, $\\dfrac{\\pi}{4}$ and $\\dfrac{\\pi}{3}$.
\nAlternatively, one can memorise the following table:
\n| \n | $\\dfrac{\\pi}{6}$ | \n$\\dfrac{\\pi}{4}$ | \n$\\dfrac{\\pi}{3}$ | \n
| \n | \n | \n | \n |
| $\\sin$ | \n$\\dfrac{1}{2}$ | \n$\\dfrac{1}{\\sqrt{2}}$ | \n$\\dfrac{\\sqrt{3}}{2}$ | \n
| \n | \n | \n | \n |
| $\\cos$ | \n$\\dfrac{\\sqrt{3}}{2}$ | \n$\\dfrac{1}{\\sqrt{2}}$ | \n$\\dfrac{1}{2}$ | \n
| \n | \n | \n | \n |
| $\\tan$ | \n$\\dfrac{1}{\\sqrt{3}}$ | \n$1$ | \n$\\sqrt{3}$ | \n
From the above, the triangle in the first quadrant tells us that:
\n$\\sin\\left(\\var{phiraddisplay}\\right)=\\;\\;\\dfrac{1}{2}$$\\sin\\left(\\var{phiraddisplay}\\right)=\\dfrac{1}{\\sqrt{2}}$$\\sin\\left(\\var{phiraddisplay}\\right)=\\dfrac{\\sqrt{3}}{2}$
\n$\\cos\\left(\\var{phiraddisplay}\\right)=\\dfrac{\\sqrt{3}}{2}$$\\cos\\left(\\var{phiraddisplay}\\right)=\\dfrac{1}{\\sqrt{2}}$$\\cos\\left(\\var{phiraddisplay}\\right)=\\;\\;\\dfrac{1}{2}$
\n$\\tan\\left(\\var{phiraddisplay}\\right)=\\dfrac{1}{\\sqrt{3}}$$\\tan\\left(\\var{phiraddisplay}\\right)=\\;\\;1$$\\tan\\left(\\var{phiraddisplay}\\right)=\\sqrt{3}$
\nSince $\\theta=\\var{thetadisplay}$ puts us {textquadrant}, the $x$-coordinate (the cosine value) is positive,negative, and the $y$-coordinate (the sine value) is positivenegative. That is:
\n$\\sin\\left(\\var{thetadisplay}\\right)=\\phantom{-}\\sin\\left(\\var{phiraddisplay}\\right)=\\;\\;\\phantom{-}\\dfrac{1}{2}$$\\sin\\left(\\var{thetadisplay}\\right)=\\phantom{-}\\sin\\left(\\var{phiraddisplay}\\right)=\\phantom{-}\\dfrac{1}{\\sqrt{2}}$$\\sin\\left(\\var{thetadisplay}\\right)=\\phantom{-}\\sin\\left(\\var{phiraddisplay}\\right)=\\phantom{-}\\dfrac{\\sqrt{3}}{2}$
\n$\\cos\\left(\\var{thetadisplay}\\right)=-\\cos\\left(\\var{phiraddisplay}\\right)=-\\dfrac{\\sqrt{3}}{2}$$\\cos\\left(\\var{thetadisplay}\\right)=-\\cos\\left(\\var{phiraddisplay}\\right)=-\\dfrac{1}{\\sqrt{2}}$$\\cos\\left(\\var{thetadisplay}\\right)=-\\cos\\left(\\var{phiraddisplay}\\right)=\\;\\;-\\dfrac{1}{2}$
\n$\\tan\\left(\\var{thetadisplay}\\right)=-\\tan\\left(\\var{phiraddisplay}\\right)=-\\dfrac{1}{\\sqrt{3}}$$\\tan\\left(\\var{thetadisplay}\\right)=-\\tan\\left(\\var{phiraddisplay}\\right)=\\;\\;-1$$\\tan\\left(\\var{thetadisplay}\\right)=-\\tan\\left(\\var{phiraddisplay}\\right)=-\\sqrt{3}$
\n$\\sin\\left(\\var{thetadisplay}\\right)=-\\sin\\left(\\var{phiraddisplay}\\right)=\\;\\;-\\dfrac{1}{2}$$\\sin\\left(\\var{thetadisplay}\\right)=-\\sin\\left(\\var{phiraddisplay}\\right)=-\\dfrac{1}{\\sqrt{2}}$$\\sin\\left(\\var{thetadisplay}\\right)=-\\sin\\left(\\var{phiraddisplay}\\right)=-\\dfrac{\\sqrt{3}}{2}$
\n$\\cos\\left(\\var{thetadisplay}\\right)=-\\cos\\left(\\var{phiraddisplay}\\right)=-\\dfrac{\\sqrt{3}}{2}$$\\cos\\left(\\var{thetadisplay}\\right)=-\\cos\\left(\\var{phiraddisplay}\\right)=-\\dfrac{1}{\\sqrt{2}}$$\\cos\\left(\\var{thetadisplay}\\right)=-\\cos\\left(\\var{phiraddisplay}\\right)=\\;\\;-\\dfrac{1}{2}$
\n$\\tan\\left(\\var{thetadisplay}\\right)=\\phantom{-}\\tan\\left(\\var{phiraddisplay}\\right)=\\phantom{-}\\dfrac{1}{\\sqrt{3}}$$\\tan\\left(\\var{thetadisplay}\\right)=\\phantom{-}\\tan\\left(\\var{phiraddisplay}\\right)=\\phantom{-}\\;\\;1$$\\tan\\left(\\var{thetadisplay}\\right)=\\phantom{-}\\tan\\left(\\var{phiraddisplay}\\right)=\\phantom{-}\\sqrt{3}$
\n$\\sin\\left(\\var{thetadisplay}\\right)=-\\sin\\left(\\var{phiraddisplay}\\right)=\\;\\;-\\dfrac{1}{2}$$\\sin\\left(\\var{thetadisplay}\\right)=-\\sin\\left(\\var{phiraddisplay}\\right)=-\\dfrac{1}{\\sqrt{2}}$$\\sin\\left(\\var{thetadisplay}\\right)=-\\sin\\left(\\var{phiraddisplay}\\right)=-\\dfrac{\\sqrt{3}}{2}$
\n$\\cos\\left(\\var{thetadisplay}\\right)=\\phantom{-}\\cos\\left(\\var{phiraddisplay}\\right)=\\phantom{-}\\dfrac{\\sqrt{3}}{2}$$\\cos\\left(\\var{thetadisplay}\\right)=\\phantom{-}\\cos\\left(\\var{phiraddisplay}\\right)=\\phantom{-}\\dfrac{1}{\\sqrt{2}}$$\\cos\\left(\\var{thetadisplay}\\right)=\\phantom{-}\\cos\\left(\\var{phiraddisplay}\\right)=\\;\\;\\phantom{-}\\dfrac{1}{2}$
\n$\\tan\\left(\\var{thetadisplay}\\right)=-\\tan\\left(\\var{phiraddisplay}\\right)=-\\dfrac{1}{\\sqrt{3}}$$\\tan\\left(\\var{thetadisplay}\\right)=-\\tan\\left(\\var{phiraddisplay}\\right)=\\;\\;-1$$\\tan\\left(\\var{thetadisplay}\\right)=-\\tan\\left(\\var{phiraddisplay}\\right)=-\\sqrt{3}$
\nAn alternative approach is to use the mnemonic \"All Stations To Central\" or \"ASTC\" to recall which trig functions are positive in each quadrant (and hence which are negative):
\n
The exact value of $\\cos\\left(\\var{thetadisplay}\\right)$ is [[1]].
\nIf $\\tan\\left(\\var{thetadisplay}\\right)$ is defined, what is its exact value? Otherwise, enter undefined [[2]].