25.08.2021 Views

082-Engineering-Mathematics-Anthony-Croft-Robert-Davison-Martin-Hargreaves-James-Flint-Edisi-5-2017

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

3.6 Trigonometric identities 125

or

sinc(x)=0whenx=±nforn=1,2,3,...

The plot ofthe normalized sincfunction isshown inFigure 3.14.

Sinc x

1

0.75

0.5

0.25

–15 –10 –5 5 10

x

15

–0.25

Figure3.14

The sincfunctionwith normalization.

3.6 TRIGONOMETRICIDENTITIES

We have seen that tanθ = sinθ for all values of θ. We call this an identity. In an

cos θ

identity, the l.h.s. and the r.h.s. are always equal, unlike in an equation where the l.h.s.

and the r.h.s. are equal only for particular values of the variable concerned. Table 3.1

listssome common trigonometric identities.

Example3.3 Simplify

cotA

cosA

Solution We know that

tanA= sinA

cosA

and so

cotA= 1

tanA = cosA

sinA

Hence

cotA

cosA =cotA× 1

cosA

= cosA

sinA × 1

cosA

= 1

sinA

This may alsobewritten as cosecA.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!