=√2(sinx*√2/2+cosx*√2/2)=√2(sinxcosπ/4+cosxsinπ/4)=√2sin(x+π/4)
(x2+ax+5）·（-6x3）=-6x^5-6ax^4-30x3不含x的四次方项所以系数为0-6a=0a=0原式=6a2-2ab-3a2-4ab+1/2b2=3a2-6ab+1/2b2
