Помогите решить алгебру легкое))) Срочно буду очень благодарен)

sin^2(a)=1-cos^2(a)=1- 25/169=144/169; sina <0; sin(a)=-12/13; ctg(a)=cos(a)sin(a)=(-5/13):(-12/13)=5/12; cos(2a)=cos^2(a)-sin^2(a)=25/169 -144/169= -119/169.

4)sina=-√1-25/169=-√144/169=-12/13ctga=-5/13:(-12/13)=5/13*13/12=5/12cos2a=25/169-144/169=-119/1695)cos(180+45)=-cos45=-√2/26)Sin(90+15)=sos15=√(1/2-√3/4)7)(cos3asin2a+sin3aCos2a)/sin2acos2a*1/2sim5acos4a=2sin5a/(sin4a*2sin5acos4a)=2/sin8a8)(4sin²acos²a-4cos²a)/(4sin²acos²a+4cos²a-4)=4cos²a(sin²a-1)/(4sin²acos²a+4(cos²a-1))=-4sin^4a/4sin²acos²a-4sin²a)=-4sin^4a/4sin²a(cos²a-1)=-4sin^4a/-4sin^4a=19)сos20*1/2(cos40-cos60)=cos20*1/2(cos40-1/2)=1/2cos40cos20-1/4cos20=1/2*2cos30cos10-1/2cos20=√3/2*cos10-1/2cos20