Topic: Factoring

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Answers
$1: 3(x^2+9)$
$2: 10(x^2+y^2)$
$3: 2x^8(6x-7)$
$4: 2x^3y^5(7y^2+3x^8)$
$5: x(11x^2+10x+1)$
$6: (x-10)(x+4)$
$7: (x-1)(x-10)$
$8: (x+4)^2$
$9: (x-9)^2$
$10: (3x+5)(x-4)$
$11: (x-4)(5x-3)$
$12: (2x+5)(3x+4)$
$13: (8x-3)^2$
$14: (4x-1)(x+4)$
$15: (5x+1)(5x-1)$
$16: (7+x)(7-x)$
$17: 2(x+10)(x-10)$
$18: 3(x+4)(x-4)$
$19: 8(x+y)(x-y)$
$20: 4(x-5)(x+1)$
$21: 3(2x+1)(x+4)$