sin a+cos a=1/3
(sina+cosa)²=(1/3)²
sin²a+2sinacosa+cos²a=1/9
1+2sinacosa=1/9
2sinacosa=1/9 -1
sin2a=-8/9
27sinacosa=13.5*2sinacosa=13.5sin2a
13.5*(-8/9)=-12
sin a+cos a=1/3
(sina+cosa)²=(1/3)²
sin²a+2sinacosa+cos²a=1/9
1+2sinacosa=1/9
2sinacosa=1/9 -1
sin2a=-8/9
27sinacosa=13.5*2sinacosa=13.5sin2a
13.5*(-8/9)=-12