C=90°
AC=4
AB=10
勾股定理：AC²+BC²=AB²
BC=√(AB²-AC²) = √(10²-4²) = 2√21
sinB = AC/AB = 4/10 = 2/5
B = arcsin(2/5)
A = π/2 - B = π/2 - arcsin(2/5)arcsin是什么反三角函数，没学过的话可以这样sinB = AC/AB = 4/10 = 0.4查三角函数表：B ≈ 23°33′A = 90° - B ≈ 66°27′