For
with
, the value of
is
. Therefore, the correct answer is C.
Given
, and since
is in the first quadrant (0° <
< 90°), you can use the fact that
to find the value of
.
![\[ \cos \theta = √(1 - \sin^2 \theta) \]\[ \cos \theta = \sqrt{1 - \left((21)/(29)\right)^2} \]\[ \cos \theta = \sqrt{1 - (441)/(841)} \]\[ \cos \theta = \sqrt{(841 - 441)/(841)} \]\[ \cos \theta = \sqrt{(400)/(841)} \]\[ \cos \theta = \pm (20)/(29) \]](https://img.qammunity.org/2019/formulas/mathematics/middle-school/2inaothj7ajkrnfgnlzluht2s95ag6rhca.png)
Since
is in the first quadrant (0° <
< 90°), the cosine is positive. Therefore, the correct answer is:
![\[ \cos \theta = (20)/(29) \]](https://img.qammunity.org/2019/formulas/mathematics/middle-school/tmcpf82ouqw5p7fgqzj4dlc66dbhs1qpww.png)
So, the answer is C.
.