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Calculus- Early Transcendentals, 2021a

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2.7. Hyperbolic Functions 69<br />

e x = 2y ± √ 4y 2 − 4<br />

2<br />

e x = y ± √ y 2 − 1<br />

From the last equation, we see y 2 ≥ 1, and since y ≥ 0, it follows that y ≥ 1.<br />

Now suppose y ≥ 1, so y ± √ y 2 − 1 > 0. Then x = ln(y ± √ y 2 − 1) is a real number, and y = coshx,<br />

so y is in the range of cosh(x).<br />

♣<br />

Definition 2.31: Hyperbolic Functions<br />

We can also define hyperbolic functions for the other trigonometric functions as you would expect:<br />

tanhx = sinhx<br />

coshx<br />

cschx = 1<br />

sinhx<br />

sechx = 1<br />

coshx<br />

cothx = 1<br />

tanhx<br />

The graph of sinhx is shown below:<br />

The graph of coshx is shown below:

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