發新話題
打印

三角函數的題目!!拜託一下

sinA = sin(C + 90度) = cosC

a + c = √2b
sinA + sinC = √2sinB

cosC + sinC = √2sin(180度 - A - C) = √2sin(90度 - 2C) = √2cos2C = √2[(cosC)^2 - (sinC)^2]
1 = √2(cosC - sinC)
(cosC - sinC)^2 = 1/2
1 - sin2C = 1/2
C = 15度

(cosC)^2 = (2 + √3)/4

TOP

發新話題