1) (c-t)² =c² -2ct+t²
2) (5b-n²)²=25b² -10bn² +n⁴
3) (2a+k)² =4a²+4ak+k²
4) (6a+0.7b³)²=36a² +8.4ab³+0.49b⁶
5) x⁴-60x²+900=(x² -30)²
6) 2a³ +4a² +2a=2a(a²+2a+1)=2a(a+1)²
7) 49x² -8x-(9+42x+49x²)=x-26
49x² -8x-9-42x-49x²-x+26=0
-51x+17=0
-51x= -17
x= -17/-51
x=1/3