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Two urgent needs of mathematics in senior one! ! ! ! !
1.(1) SINA SINB-COSA COSB =-COS (A+B), because A and B∈(π/4, π/2), A+B in (π/2, π), COS (A+B) & 0,Sina sinb-cosa cosb & gt; 0.sinAsinB & gtcosAcosB .

(2) vector a* vector b= 1, that is, the root number 3*sinA-cosA= 1, cos(A+π/3)=- 1/2, and because of 0.

2. "Let the equation sin(3π-a)= radical number 2*cos(3π-b),

Is the radical number 3*cos(-a)=- radical number 2 *sin(π+B) also true? ",if it is, it should not be a definite value, are you giving less conditions?