Bài 1:
a) \(\left(n+2\right)^2-\left(n-2\right)^2=n^2+4n+4-\left(n^2-4n+4\right)=8n\) \(⋮\)\(8\) (đpcm)
b) \(\left(n+7\right)^2-\left(n-5\right)^2=n^2+14n+49-\left(n^2-10n+25\right)=24n-24\)\(⋮\)\(24\) (đpcm)
Bài 2:
mk biến đổi về pt tích sau đó bạn giải nốt nhé
a) \(\left(x-4\right)^2-36=0\)
<=> \(\left(x-4-6\right)\left(x-4+6\right)=0\)
<=> \(\left(x-10\right)\left(x+2\right)=0\)
................
b) \(4x^2-12x=-9\)
<=> \(4x^2-12x+9=0\)
<=> \(\left(2x-3\right)^2=0\)
..............
c) \(\left(x+8\right)^2=121\)
<=> \(\left(x+8\right)^2-121=0\)
<=> \(\left(x+8+11\right)\left(x+8-11\right)=0\)
<=> \(\left(x+19\right)\left(x-3\right)=0\)
...................
Bài 3:
a) \(31,8^2-2\times31,8\times21,8+21,8^2\)
\(=\left(31,8-21,8\right)^2=10^2=100\)
b) mạo phép chỉnh đề
\(58,2^2+2\times58,2\times41,8+41,8^2\)
\(=\left(58,2+41,8\right)^2=100^2=10000\)