1)由单位圆知道,斜边为1,∴cosa=√2/10,cosb=2/√5
∵a和b都是锐角,∴sina=√如唤铅(102-2)/10=(7√2)/10,sinb=√(5-4)/√5=1/√5
∴tana=(7√2)/√2,tanb=1/2
∴tan(a+b)=(tana+tanb)/(1-tanatanb)=(7+1/2)/(1-7*1/2)=-3
2)tan2b=2tanb/(1-tan2b)=4/3,
tan(a+2b)=(tana+tanb)/(1-tanatanb)=-1
a+2b=π-π/4或2π-π/4
∵a,b是锐角,tan(a+2b)是负值,∴π/2
∴a+2b=π-π/渣好链型4=3π/4