Question

cho sin(a+b)=1,sin(a-b)=\(\dfrac{1}{2}\).tính sin a .cos b

Answer 1

Tham khảo

sin(a+b) = sina.cosb + cosa.sinb = 1, suy ra cosa.sinb = 1 - sina.cosb.

sin(a-b) = sina.cosb - cosa.sinb = sina.cosb - (1 - sina.cosb) = 2sina.cosb - 1=1/2.

Vậy sina.cosb=(1/2+1):2=3/4.