câu này mới đúng nha
a/\(\left(x-25\right)^2=\left(x^2-2x25-25^2\right)=x^2-50x+25^2\)
b/\(25-\left(3-x^2\right)=5^2-\left(3-x\right)^2\)
=\(\left(5-3-x\right).\left(5+3-x\right)\)
=(2-x).(8-x)
= 16 - 2x -8x +x2
=\(8\left(2-x\right)+x\left(-2+x\right)\)
= -8(-2+x) + x(-2+x)
= (-2+x)(-8+x)
c/ \(\left(7x-4\right)^2-\left(12x+1\right)^2\)
=( 7x-4- 12x-1)(7x-4+12x+1)
=(-5x-5)(19x-3)
=\(-95x^2+15x-95x+15\)
= -95x(x+1) + 15(x+1)
=(x+1)(-95x+15)
A=(x-25)2=(x-25)(x-25)
B=25-(3-x)2=52-(3-x)2=(5-3+x)(5+3-x)=(2-x)(8-x)
C=(7x-4)2-(12x+1)2
= (7x-4-12x-1)(7x-4+12x+1)
= (-5x-5)(19x-3)
=-5(x+1)(19x-3)
D=49(y-4)2-49(y+2)2
=49((y-4)2-(y+2)2)
= 49(y-4-y-2)(y-4+y+2)
=49.2(2y-2)
=49.2.2(y-1)
=196(y-1)
bạn nhớ theo dõi và tick cho mk nhé 
a/\(\left(x-25\right)^2=x^2-2.x.25+25^2=x^2-50x+25^2\)
b/\(25-\left(3-x\right)^2=5^2-\left(3-x\right)^2=\left(5-3-x\right)\left(5+3-x\right)=\left(2-x\right).\left(8-x\right)=16-2x-8x+x^2=8\left(2-x\right)+x\left(-2+x\right)=-8\left(-2+x\right)+x\left(-2+x\right)=\left(-2+x\right)-\left(8-x\right)\)
c/\(\left(7x-4\right)^2-\left(12x+1\right)^2\)
=\(\left(7x-4-12x-1\right)\left(7x-4+12x+1\right)\)
=\(\left(-5x-5\right)\left(19x-3\right)=-95x^2+15x-95x+15\)
=\(-95x\left(x+1\right)+15\left(x+1\right)=\left(x+1\right)\left(-95x+15\right)\)
d/\(49\left(y-4\right)^2-9\left(y+2\right)^2\)
=\(49\left[\left(y-4\right)^2-\left(y+2\right)^2\right]\)
=\(49\left(y-4-y-2\right)\left(y-4+y+2\right)\)
=\(49.2\left(2y-2\right)\)
=\(49.2.2\left(y-1\right)\)
=\(196\left(y-1\right)\)
nếu thấy đúng thì tick nha!