5.a)25a²+10a+1=(5a+1)²
b)4x²-12xy+9y²=(2x-3y)²
c)36m²+12m+1=(6m+1)²
d)9a²-30a+25=(3a-5)²
e)1-10x+25x²=(1-5x)²
7.a)(y+1)²-4y=-5+(y-2)²
y²+1+2y-4y=-5+y²+4-4y
y²+2y-4y-y+4y=-5+4-1
2y=-1
y= - 1
b)(3x+1)(x-1)-2x²=(x+2)²-5
3x²-3x+x-1-2x²=x²+4+4x-5
6x=0
x=0