### Home > A2C > Chapter 8 > Lesson 8.2.2 > Problem8-136

8-136.

Find the value of $x$ in each triangle.

1. Use the Law of Cosines.

$\left(x\right)^{2} = \left(15\right)^{2} + \left(21\right)^{2} − 2\left(15\right)\left(21\right)\operatorname{cos}\left(40°\right)$

$x=\sqrt{666-630\text{ cos}(40º)}$

$x ≈ 13.542$

1. Find the last angle, then use the Law of Sines.

$x ≈ 68.770$