A² -b² =(a -b)(a +b)
a) (a²+2ab+b²) -c² = (a+b)² -c² =(a+b -c)(a+b +c)
b) 49 -m² -2mn -n² =49 - (m +n)² =(7 -(m+n)(7 +m+n) =(7 -m -n)(7 +m +n)
13. a) x² -2xc +c² -d² = (x -c)² -d² =(x-c -d)(x-c +d)
25. a² +2ab +b² =(a +b)²
a) 28² +2*28*34 +34² = (28 +34)² =62² =3 844
a² -2ab +b² =(a -b)²
b) 27² -2*27*13 +13² = (27 -13)² =14² =196