// Numbas version: finer_feedback_settings {"name": "Exact values for sin, cos, tan (0 to 330, degrees)", "extensions": ["geogebra"], "custom_part_types": [], "resources": [["question-resources/exact_values.svg", "exact_values_HBd4LtO.svg"], ["question-resources/ASTCwhite.png", "ASTCwhite_0FVod00.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 330, degrees)", "tags": ["trig", "trigonometry", "Trigonometry"], "metadata": {"description": "
exact value of sin, cos, tan of random(0,90,120,135,150,180,210,225,240,270,300,315,330) degrees
", "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 $\\sin(60^\\circ)$, which is $\\dfrac{\\sqrt{3}}{2}$, you would input sqrt(3)/2
", "advice": "Recall the unit circle definitions:
\nIn particular, the angle of $\\var{theta}^\\circ$ 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 $(\\var{cos({theta}*pi/180)}, \\var{sin({theta}*pi/180)})$. From these, we can conclude that
\n$\\sin(\\var{theta}^\\circ)=\\var{sin({theta}*pi/180)}$,
\n$\\cos(\\var{theta}^\\circ)=\\var{cos({theta}*pi/180)}$, and
\n$\\tan(\\var{theta}^\\circ)=\\dfrac{\\sin(\\var{theta}^\\circ)}{\\cos(\\var{theta}^\\circ)}=\\dfrac{\\var{sin({theta}*pi/180)}}{\\var{cos({theta}*pi/180)}}\\var{if(theta=90 or theta=270, \" which is undefined\",\" = \" + precround(tan(theta*pi/180),0))}.$
\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 $30^\\circ$, $45^\\circ$ and $60^\\circ$.
Alternatively, one can memorise the following table:
\n| \n | $30^\\circ$ | \n$45^\\circ$ | \n$60^\\circ$ | \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(\\var{phi}^\\circ)=\\;\\;\\dfrac{1}{2}$$\\sin(\\var{phi}^\\circ)=\\dfrac{1}{\\sqrt{2}}$$\\sin(\\var{phi}^\\circ)=\\dfrac{\\sqrt{3}}{2}$
\n$\\cos(\\var{phi}^\\circ)=\\dfrac{\\sqrt{3}}{2}$$\\cos(\\var{phi}^\\circ)=\\dfrac{1}{\\sqrt{2}}$$\\cos(\\var{phi}^\\circ)=\\;\\;\\dfrac{1}{2}$
\n$\\tan(\\var{phi}^\\circ)=\\dfrac{1}{\\sqrt{3}}$$\\tan(\\var{phi}^\\circ)=\\;\\;1$$\\tan(\\var{phi}^\\circ)=\\sqrt{3}$
\nSince $\\theta=\\var{theta}^\\circ$ 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(\\var{theta}^\\circ)=\\phantom{-}\\sin(\\var{phi}^\\circ)=\\;\\;\\phantom{-}\\dfrac{1}{2}$$\\sin(\\var{theta}^\\circ)=\\phantom{-}\\sin(\\var{phi}^\\circ)=\\phantom{-}\\dfrac{1}{\\sqrt{2}}$$\\sin(\\var{theta}^\\circ)=\\phantom{-}\\sin(\\var{phi}^\\circ)=\\phantom{-}\\dfrac{\\sqrt{3}}{2}$
\n$\\cos(\\var{theta}^\\circ)=-\\cos(\\var{phi}^\\circ)=-\\dfrac{\\sqrt{3}}{2}$$\\cos(\\var{theta}^\\circ)=-\\cos(\\var{phi}^\\circ)=-\\dfrac{1}{\\sqrt{2}}$$\\cos(\\var{theta}^\\circ)=-\\cos(\\var{phi}^\\circ)=\\;\\;-\\dfrac{1}{2}$
\n$\\tan(\\var{theta}^\\circ)=-\\tan(\\var{phi}^\\circ)=-\\dfrac{1}{\\sqrt{3}}$$\\tan(\\var{theta}^\\circ)=-\\tan(\\var{phi}^\\circ)=\\;\\;-1$$\\tan(\\var{theta}^\\circ)=-\\tan(\\var{phi}^\\circ)=-\\sqrt{3}$
\n$\\sin(\\var{theta}^\\circ)=-\\sin(\\var{phi}^\\circ)=\\;\\;-\\dfrac{1}{2}$$\\sin(\\var{theta}^\\circ)=-\\sin(\\var{phi}^\\circ)=-\\dfrac{1}{\\sqrt{2}}$$\\sin(\\var{theta}^\\circ)=-\\sin(\\var{phi}^\\circ)=-\\dfrac{\\sqrt{3}}{2}$
\n$\\cos(\\var{theta}^\\circ)=-\\cos(\\var{phi}^\\circ)=-\\dfrac{\\sqrt{3}}{2}$$\\cos(\\var{theta}^\\circ)=-\\cos(\\var{phi}^\\circ)=-\\dfrac{1}{\\sqrt{2}}$$\\cos(\\var{theta}^\\circ)=-\\cos(\\var{phi}^\\circ)=\\;\\;-\\dfrac{1}{2}$
\n$\\tan(\\var{theta}^\\circ)=\\phantom{-}\\tan(\\var{phi}^\\circ)=\\phantom{-}\\dfrac{1}{\\sqrt{3}}$$\\tan(\\var{theta}^\\circ)=\\phantom{-}\\tan(\\var{phi}^\\circ)=\\phantom{-}\\;\\;1$$\\tan(\\var{theta}^\\circ)=\\phantom{-}\\tan(\\var{phi}^\\circ)=\\phantom{-}\\sqrt{3}$
\n$\\sin(\\var{theta}^\\circ)=-\\sin(\\var{phi}^\\circ)=\\;\\;-\\dfrac{1}{2}$$\\sin(\\var{theta}^\\circ)=-\\sin(\\var{phi}^\\circ)=-\\dfrac{1}{\\sqrt{2}}$$\\sin(\\var{theta}^\\circ)=-\\sin(\\var{phi}^\\circ)=-\\dfrac{\\sqrt{3}}{2}$
\n$\\cos(\\var{theta}^\\circ)=\\phantom{-}\\cos(\\var{phi}^\\circ)=\\phantom{-}\\dfrac{\\sqrt{3}}{2}$$\\cos(\\var{theta}^\\circ)=\\phantom{-}\\cos(\\var{phi}^\\circ)=\\phantom{-}\\dfrac{1}{\\sqrt{2}}$$\\cos(\\var{theta}^\\circ)=\\phantom{-}\\cos(\\var{phi}^\\circ)=\\;\\;\\phantom{-}\\dfrac{1}{2}$
\n$\\tan(\\var{theta}^\\circ)=-\\tan(\\var{phi}^\\circ)=-\\dfrac{1}{\\sqrt{3}}$$\\tan(\\var{theta}^\\circ)=-\\tan(\\var{phi}^\\circ)=\\;\\;-1$$\\tan(\\var{theta}^\\circ)=-\\tan(\\var{phi}^\\circ)=-\\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 $\\cos(\\var{theta}^\\circ)$ is [[1]].
\nIf $\\tan(\\var{theta}^\\circ)$ is defined, what is its exact value? Otherwise, enter undefined [[2]].