吹散烟圈 花朵
共回答了24个问题采纳率:95.8% 举报
1年前
天鳕方云 幼苗
共回答了252个问题 举报
sinA = a/(2R), sinB = b/(2R), sinC = c/(2R)
sinAsinB + sinBsinC + cos2B = 1
a/(2R)*b/(2R) + b/(2R) *c/(2R) + 1 - 2(sinB)^2 = 1
(a*b)/(4R^2) + (b*c)/(4*R^2) = 2 (sinB)^2 = 2*b^2/(4R^2)
所以,
a*b + b*c = 2*b^2
a + c = 2b
所以,a、b、c 成等差数列
因为 C = 90°,则 sinC = 1,c = 2R,sinA = cosB
(a+c)/(sinA+1) = 2b/(sinA+1) = b/sinB
2sinB = sinA + 1
4(sinB)^2 = 4 - 4*(cosB)^2 = (sinA)^2 + 2sinA +1 = (cosB)^2 + 2cosB + 1
5(cosB)^2 + 2cosB - 3 = 0
所以,cosB = sinA = [-2+√(2^2 + 4*5*3)]/(2*5) = [-2+8]/10 = 0.6
sinB = cosA = √[1-(sinA)^2] = 0.8
因此,a/b = sinA/sinB = 0.6/0.8 = 3/4
1年前
你能帮帮他们吗