a)
(3x+1)^2 + (4x+1)^2 = (5x+1)^2\\ 9x^2+6x+1+16x^2+8x+1=25x^2+10x+1\\ 25x^2+4x+2-25x^2-10x=1 |-2\\ 4x=-1\\ x=-\frac{1}{4}
b)
(x+2)^2-(x-2)(x+3)=8\\ x^2+4x+4-(x^2+3x-2x-6)=8\\ x^2+4x+4-x^2-x+6=8\\ 3x+10=8 |-10\\ 3x=-2 |:3 \\ x=-\frac{2}{3}
c)
(x^2-7x+6)(x^2-8x+7)=0\\ x^2-7x+6=0 \vee x^2+8x+7=0\\ x^2-6x-x+6=0\\x(x-6)-(x-6)=0\\ (x-1)(x-6)=0\\ x=1 \vee x=6
lub
x^2-8x+7=0\\ x^2-7x-x+7=0\\ x(x-7)-(x-7)=0\\ (x-1)(x-7)=0\\ x=1\vee x=7
x_1=1, \ x_2=6, \ x_3=7