### Home > CCA2 > Chapter C > Lesson C.1.3 > ProblemC-58

C-58.

Find the value of $x$ in each triangle.

1. Use the Law of Cosines.

$C²\ =\ A² + B² - 2AB\text{cos}(c)$

$(x)²\ =\ (15)² + (21)² - 2(15)(21)\text{cos}(40°)$

$x\ =\ \sqrt{666-630\text{cos}(40°)}$
$x ≈ 13.542$

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

$x ≈ 68.770$