integral of (1-tan^2x)/sec^2x, calculus 2 tutorial, trig integrals with trig identities

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Calculus 2, integral of (1-tan^2x)/sec^2x, integral of cos(2x)

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#blackpenredpen #math #calculus #apcalculus
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Wanted to share my method for this one: sec^2(x) = tan^2(x)+1. So you get tan^2(x)-1 / tan^2(x)+1, which is another identity for cos(2x) already. So, from the start, you can already transform the integral, with identities only, into Int((cos(2x)dx).

etiennedube
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lol. Got the same result but used a different approach. converted tangent and secant into their sin/cos equivalents and then did a little algebra to get cos^2(x) - sin^2(x) then split it up and used power reduction formulas to simplify. Always fun when there are multiple paths to the same solution.

pipertripp
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for those of you who are wondering how he got 2cos^2x-1 is because he split the 2-sec^2x and canceled sec^2x over sec^2x

MotivationalContent-rz
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This is potentially good news for me. I am a bit like the ancient mariner in the famous poem - 'He stoppeth one in three'. But my problem is not to do with Albatross, it's about the integral of 1 + Tan^2 (x). So in 1972 when I did U.K. A level maths, we worked out the integral and I thought to myself, 'I wonder how that is going to impact my life?' I didn't exactly phrase it in the way I've written here, largely because back in those days I was a raw numpty. So I'm always pleased to see math videos on Youtube, in the hope that I can find out how the integral of 1 + Tan^2 (x) affects our daily lives. I never did find out and I'm 70 years old now....:)

Greebstreebling
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When i see stuff like this i just think
-> convert into Trig rational form (sin and cos) -> weierstrass substitution -> Polynomial rational -> Partial Fraction

maalikserebryakov
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THANK YOU SO MUCH! Your videos have been so helpful!

marthavilla
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or write the numerator as (1+tan^2(x)-2tan^(x)/sec^2 (x)
1+tan^2 (x) is just sec^2(x)
so we are left with 1-(2tan^2x/sec^2x)
tan^2 (x)/sec^2(x) is just sin^2(x)
so only 1-2sin^2(x) is left
then integrate to get x-(x-sin2x/2)
which equals to sin2x/2 which further simplifies into sin(x)cos(x)

oh and dont forget the constant C ;)

Gawkie
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I think it's much easier and faster to solve if you separate it into 2 fractions.

saeedsaleh
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Al menos le entendí mas que a los profesores latinos

danielalopezuribe
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I multiplied cos^2(x) top and bottom.

Then get cos^2(x) - sin^2(x) = cos(2x)

And then the same as you

joaquingutierrez
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I DONT GET IT WDYM 2COS^2-1 IS HOW IM CRYING BRO.... IS IT THE HALF ANGLE IDENTITY OR WHAT IM SUPER I HATE CALCULUS

marya-d