Which equation should you solve to find x? A. COS 26 = x/10
B. COS 26 = 9/10
C. Sin 26 = x/10
D. Tan 26 = 9/x

Choice C

sin(26) = x/10

Explanation:

With respect to the 26 degree angle, the x is the opposite side and the 9 is the length of the adjacent side.

We can say tan(26) = x/9 because tangent is the ratio of opposite over adjacent. In other words, tan(angle) = opposite/adjacent

Unfortunately, tan(26) = x/9 is not an answer choice.

Luckily though, we have other trig ratios to work with.

The sine ratio ties together the opposite side and hypotenuse

sin(angle) = opposite/hypotenuse

sin(26) = x/10

Extra info (optional section)

Solving for x leads to...

sin(26) = x/10

10*sin(26) = x

x = 10*sin(26)

x = 4.38371 approximately

Also, note how cos(26) = 0.89879 approximately, which is fairly close to 9/10 = 0.9. This indicates some rounding error is going on when your teacher is displaying either the 9, the 10, or the 26 degree angle.

1/800 is the right answer