Question

在三角形ABC中,a,b,c分别是角A,B,C的对边,设a+c=2b,角A减角C等于60度,求sinB

Answer 1

在三角形ABC中, a/sinA = b/sinB = c/sinC a + c = 2b sinA + sinC = 2sinB 2sin[(A+C)/2] * cos[(A-C)/2] = 2 * 2 * sin(B/2) * cos(B/2) sin[(A+C)/2] * cos30 = 2 * sin(B/2) * cos(B/2) cos[90 - (A+C)/2] * cos...