SOLUTION: find the measure of the third side of the triangle given its 2 sides and perimeter. 1side= 7x^2 + 5x + 9 2side= 8x^2 - 6x + 12 P= 19x^2 + 12x + 35cm please help thank you!

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Question 363760: find the measure of the third side of the triangle given its 2 sides and perimeter.
1side= 7x^2 + 5x + 9
2side= 8x^2 - 6x + 12
P= 19x^2 + 12x + 35cm
please help thank you!
Answer by anantha(86) (Show Source):
You can put this solution on YOUR website!
in a triangle perimeter= sum of the 3 sides
perimeter=1st side+2nd side+3rd side
19x^2+12x+35cm=(7x^2+5x+9)+(8x^2-6x+12)+3rd side
here do addition carefully add only like terms means x^2 terms and add xterms and constant terms
19x^2+12x+35=(7x^2+8x^2)+(5x-6x)+(9+12)+3rd side
19x^2+12x+35=15x^2-x+21+3rd side
we subtract 15x^2 on both sides
19x^2-15x2+12x+35=(15x^2-15x^2)-x+21+3rd side
4x^2+12x+35=-x+21+3rd side
add x on both sides
4x^2+12x+x+35=(-x+x)+21+3rd side
4x^2+13x+35=21+ 3rd side
subtract 21 on both sides
4x^2+13x+35-21=(21-21)+ 3rd side
4x^2+13x+14=3rd side