已知sin(a-π/4)=(7√2)/10,cos2a=7/25
问题描述:
已知sin(a-π/4)=(7√2)/10,cos2a=7/25
(1)求sina+cosa
(2)求tan(a+π/3)
答
∵sin(a-π/4)=(7√2)/10∴sinacosπ/4-cosasinπ/4 =(7√2)/10∴√2/2(sina-cosa)=(7√2)/10∴sina-cosa=7/5 .(1)∵cos2a=7/25 ∴cos^2a-sin^2a=7/25∴sin^2a-cos^2a=-7/25∴(sina+cosa)(sina-cosa)=-7/2...