Answer:
2 a^4 -2a^2b^2 -6b^4
Step-by-step explanation:
C = 7a^4 + 5a^2b^2 -3b^4
D = 5a^4 +7a^2b^2 +3b^4
C-D = 7a^4 + 5a^2b^2 -3b^4 - ( 5a^4 +7a^2b^2 +3b^4)
Distribute the minus sign
7a^4 + 5a^2b^2 -3b^4 - 5a^4 -7a^2b^2 -3b^4
I like to line them up vertically
7a^4 + 5a^2b^2 -3b^4
- 5a^4 -7a^2b^2 -3b^4
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2 a^4 -2a^2b^2 -6b^4
