已知tan(π+α)=1/7,sin(3π/2+β)=-3√10/10,α,β均為銳角,
tan(π+α)=1/7
tanα=1/7
sinα/cosα=1/7
7sinα=cosα
7sinα=√1-sin²α
49sin²α=1-sin²α
sin²α=1/50
sinα=√2/10
cosα=7√2/10
2sin²α-sinαcosα
=2sin²α-sinα*7sinα
=-5sin²α
=-5*1/50
=-1/10
sin(3π/2+β)=-3√10/10
cosβ=3√10/10
β