Explanation:
we use the law of sine :
a/sin(A) = b/sin(B) = c/sin(C)
a, b, c being the sides, A, B, C being the opposing angles of the sides.
and remember, the sum of all angles in a triangle is 180°.
so,
JL/sin(90) = KL/sin(72)
JL/1 = KL/sin(72)
KL = JL × sin(72) = 10 × 0.951056516... =
= 9.51056516... ≈ 10
JK/sin(L) = JL/sin(90) = JL
JK = JL × sin(L)
angle L = 180 - 90 - 72 = 18°
JK = JL × sin(18) = 10 × 0.309016994... =
= 3.09016994... ≈ 3