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40 votes
40 votes
Prove that sin^4x + cos^4x= sinxcosx

User Monie
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1 Answer

20 votes
20 votes

Answer:

(the relation you wrote is not correct, there may be something missing, so I will simplify the initial expression)

Here we have the equation:


image

We can rewrite this as:


image

Now we can add and subtract cos^2(x)*sin^2(x) to get:


image

We can complete squares to get:


image

and we know that:

cos^2(x) + sin^2(x) = 1

then:


image

This is the closest expression to what you wrote.

We also know that:

sin(x)*cos(x) = (1/2)*sin(2*x)

If we replace that, we get:


image

Then the simplification is:


image

User Morbusg
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3.1k points