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Solution 2.1:6d
From Förberedande kurs i matematik 1
First, we simplify the numerator and denominator for the whole fraction by rewriting as
a−b
a+ba+b+b2a+b=a+b
a−b
a+b
+b2a+ba2−b2+b2=a2a+b
a+ba−b
2=1−
a+b
2
a−b
2=
a+b
2
a+b
2−
a+b
2
a−b
2=
a+b
2
a+b
2−
a−b
2=
a+b
2
a2+2ab+b2
−
a2−2ab+b2
=4ab
a+b
2
The whole fraction is therefore
a+ba−b
2a−b+b2a+b=a2a+b4ab
a+b
2=a2a+b
4ab
a+b
2=4ba
a+b