16. 25-x2=(5-x)(5+x)
17. -144+y2=(y-12)(y+12)
18. -196+4x2=(2x-14)(2x+14)=2.(x-7).2(x+7)=4(x-7)(x+7)
19. 25x2-2252=(5x-225)(5x+225)
20.26-47x2=\(\left(8-\sqrt{47}x\right)\left(8+\sqrt{47}x\right)\)
21.-48+36y2=(6y-256)(6y+256)
26: \(\left(x+3\right)^2-16=x^2+6x+9-16=x^2+6x-7\)
27: \(64+\left(-49y^2\right)=\left(8-7y\right)\left(8+7y\right)\)
28: \(4x^2-\left(y+2\right)^2=\left(2x-y-2\right)\left(2x+y+2\right)\)