# Inverse Functions & Trig. Equations

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7. Evaluate sin[sin^-1(-1/2)].
a. 1/2
b. ð /6
c. -1/2
d. - ð /6

8. Evaluate cos[tan^-1(5/12)].
a. 12/13
b. 12/5
c. 5/12
d. 5/13

9. Evaluate cos[sin^-1(-3/5)].
a. -4/5
b. 5/4
c. 4/5
d. -3/4

• Inverse Functions & Trig. Equations -

I don't know at what level you have studied inverse trig functions, but Sal Khan has hundreds of very simple videos on Youtube.

first of all sin^-1 (-3/5) to me means ..
give me the angle Ø so that sinØ = -3/5
and since sin (of angle) = opposite/hypotenuse, I see the famous 3-4-5 triangle.
But since the sine is negative, I could sketch that triangle in quadrants III or IV,
(I will pick IV since -Ø is the smallest angle)
so now we want
cos(the angle of that triangle) = adj/hyp = 4/5

Of course you could just blindly let your calculator do the work for you ...
on mine :
2nd F
sin
(-3/5)
=
cos
=
and I got 0.8 which is 4/5

Now do #2 the same way.

BTW, wouldn't #1 be -1/2 by the
"Just look at it" Theorem ?

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