<span>1-cos2a= </span>1-2cos^2a-1= -2cos^2a
N°1
а)(a+5)²=a²+2*a*5+5²=a²+10a+25
б)(3y-x)²=(3y)²-2*3y*x+x²=9y²-6xy+x²
в)(2b-1)(2b+1)=(2b)²-1²=4b²-1
г)(4a+3b)(4a-3b)=(4a)²-(3b)²=16a²-9b²
N°2
а)b²-16=b²-4²=(b+4)(b-4)
б)a²+6a+9=a²+2*a*3+3²=(a+3)²
в)49в²b⁴-100c⁴=(7вb²)²-(10c²)²=(7вb²+10c²)(7вb²-10c²)
г)(x+1)²+(x-1)²=x²+2*x*1+1²+x²-2*x*1+1²=x²+2x+1+x²-2x+1=2x²+2
N°3
(a-3)²-3a(a-2)=a²-2*a*3+3²-3a²+6a=a²-6a+9-3a²+6a=-2a²+9