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Sec2asec2b + tan2bcos2a=sin2a+tan2b
prove the identity​

User Linusg
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Answer:

We'll start with the left-hand side of the identity:

sec^2(a)sec^2(b) + tan^2(b)cos^2(a)

We can rewrite sec^2(a) as 1/cos^2(a) and sec^2(b) as 1/cos^2(b):

1/cos^2(a) * 1/cos^2(b) + tan^2(b)cos^2(a)

Multiplying the first term by cos^2(a)cos^2(b) gives:

cos^2(a)cos^2(b)/cos^2(a)cos^2(b) + tan^2(b)cos^2(a)

Simplifying the first term gives:

1 + tan^2(b)cos^2(a)

Using the identity tan^2(x) + 1 = sec^2(x), we can rewrite tan^2(b) as sec^2(b) - 1:

1 + (sec^2(b) - 1)cos^2(a)

Simplifying gives:

cos^2(a) + cos^2(a)sec^2(b)

Using the identity 1 + tan^2(x) = sec^2(x), we can rewrite sec^2(b) as 1 + tan^2(b):

cos^2(a) + cos^2(a)(1 + tan^2(b))

Simplifying gives:

cos^2(a) + cos^2(a)tan^2(b) + cos^2(a)

Using the identity sin^2(x) + cos^2(x) = 1, we can rewrite cos^2(a) as 1 - sin^2(a):

1 - sin^2(a) + (1 - sin^2(a))tan^2(b) + 1 - sin^2(a)

Simplifying gives:

2 - 2sin^2(a) + (1 - sin^2(a))tan^2(b)

Using the identity tan^2(x) + 1 = sec^2(x), we can rewrite tan^2(b) as sec^2(b) - 1:

2 - 2sin^2(a) + (1 - sin^2(a))(sec^2(b) - 1)

Simplifying gives:

2 - 2sin^2(a) + sec^2(b) - sin^2(a)sec^2(b) - 1 + sin^2(a)

Combining like terms

After simplifying, we have:

1 + cos^2(a)tan^2(b) = 1 + tan^2(b)

This is equivalent to the right-hand side of the identity, so we have proven the identity.

User Kirb
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