Question

已知tana=2,求下列各式的值3sina^2-2sinacosa-1

Answer 1

3sin²a-2sinacosa-1

=(3sin²a-2sinacosa)/(sin²a+cos²a)-1

分子分母同时除以cos²a

=(3tan²a-2tana)/(tan²a+1)-1

=(3*2²-2*2)/(2²+1)-1

=8/5-1

=3/5