cchui7
幼苗
共回答了196个问题 举报
tan(a+π/4)=2,
tana=tan[(a+π/4)-π/4]=[tan(a+π/4)-tan(π/4)]/[1+tan(a+π/4)tan(π/4)]=(2-1)/(1+2×1)=1/3,
(1+2sinacosa)/(cos^2a-sin^2a)=(cos^2a+sin^2a+2sinacosa)/(cos^2a-sin^2a)=(1+tan^2a+2tana)/(1-tan^2a)
=[1+(1/3)^2+2×(1/3)]/[1-(1/3)^2]=(16/9)/(8/9)=2
1年前
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