` a) ` ` 36(x + 5)^2 - 25(2x - 3)^2 `
` = 6^2 (x + 5)^2 - 5^2 (2x - 3)^2 `
` = (6x + 30)^2 - (10x - 15)^2 `
` = (6x + 30 - 10x + 15)(6x + 30 + 10x - 15) `
` = (45 - 4x)(16x - 15) `
` b) ` ` 81(x + 5)^2 - 49 `
` = 9^2 (x + 5)^2 - 7^2 `
` = (9x + 45)^2 - 7^2 `
` = (9x + 45 - 7)(9x + 45 + 7) `
` = (9x + 38)(9x + 52) `
` c) ` ` x^6 - y^6 `
` = (x^4 - y^4)(x^4 + y^4) `
` = (x^2 - y^2)(x^2 + y^2)(x^4 + y^4) `
` = (x - y)(x + y)(x^2 + y^2)(x^4 + y^4) `
` d) ` ` (x + y)^2 + 8(x + y) + 16 `
` = (x + y)^2 + 2.(x + y).4 + 4^2 `
` = (x + y + 4)^2 `
