(1) COS(PI/4-A)=√2/10 ∴COSA+SINA=1/5 ∵COSA^2+SINA^2=1∴解得(5SINA-4)(5SINA+3)=0
∴SINA=4/5,SINA=-3/5(不合)
(2)若△ABC的面积S=12=1/2absinc ∴aSINC=4 a=4/SINC
(1) COS(PI/4-A)=√2/10 ∴COSA+SINA=1/5 ∵COSA^2+SINA^2=1∴解得(5SINA-4)(5SINA+3)=0
∴SINA=4/5,SINA=-3/5(不合)
(2)若△ABC的面积S=12=1/2absinc ∴aSINC=4 a=4/SINC