Tìm x biết: x + 2 = (x + 2)^2

1.Tim x biet: x+2=(x+2)^2
3.CMR;
a)7^19+7^20+7^21 cung chia het cho 57
b)x^2+2x+2>0 voi moi x
c)x^2-3x+4>o voi moi x.Please,help me!!!!!