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TMUA 2021 · Paper 2 · Question 5
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On which line is the first error in the following argument?
---
A
sin
2
x
+
cos
2
x
=
1
for all values of
x
.
B
Therefore
cos
x
=
1
−
sin
2
x
for all values of
x
.
C
Hence
1
+
cos
x
=
1
+
1
−
sin
2
x
for all values of
x
.
D
Thus
(
1
+
cos
x
)
2
=
(
1
+
1
−
sin
2
x
)
2
for all values of
x
.
E
Substituting
x
=
π
gives
0
=
4
.
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