SUBTRACTING POLYNOMIALS

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[tex]\sf (20x^2+10a+a^2-14a^3)-(x^2-5x+15)[/tex]

Step 1: Change the terms which are negative to positive and the positive to negative and change the operation to addition.

[tex]\sf (20x^2+10a+a^2-14a)+(-x^2+5x-15)[/tex]

Step 2: Add the like terms or the terms with the same variable and exponent.

[tex]\sf (20x^2-x^2)+(a^2)+(10a)+(5x)+(-15)[/tex]

[tex]\sf \boxed{\sf 19x^2+a^2+10a+5x-15}[/tex]

↬  Hence, the answer is 19x^2 + a^2 + 10a + 5x - 15