已知tanx=2求下列各式的值(1)2/3sin2x+1/4cos2x(2)2sin2x-sinxcosx+cos2x

Answer 1

1)2/3sin2x+1/4cos2x=[2/3*2sinxcosx+1/4(cos²x-sin²x)]/(sin²x+cos²x) 两边同除以cos²x=(4/3tanx+1/4-1/4tan²x)/(tan²x+1)∵tanx=2∴原式=（4/3*2+1/4-1/4*2²）/（2²...