If a= (√3-√2)/ (√3+√2) and b = (√3+√2)/ (√3-√2), find the value of a2+b2-5ab
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Answer:
a=
3
+
2
3
−
2
b=
3
−
2
3
+
2
ab=
3
×
2
3
−
2
×
3
−
2
3
+
2
=1
a+b=
3
+
2
3
−
2
+
3
−
2
3
+
2
=
(
3
+
2
)(
3
−
2
)
(
3
−
2
)
2
+(
3
+
2
)
2
=
3−2
5−2
6
+5+2
6
=10
Now, (x+y)
2
=x
2
+y
2
+2xy
⇒x
2
+y
2
=(x+y)−2xy
Replace x=a,y=b
a
2
+b
2
=(a+b)
2
−2ab
=(10)
2
−2×1
(x+y)=10 and xy=1
=100−2=98
a
2
+b
2
−5ab=98−5×1
=98−5
=93
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