Question

find local maxima and local minima for the function f(x)=sin x-cos x
0 13 years ago

Answer 1

@hartnn

Answer 2

for this you have to find f'(x)

Answer 3

ok ....cos x + sin x
then?

Answer 4

and then take f'(x)=0

Answer 5

sin x+cos x=0

Answer 6

sinx=-cos x

Answer 7

nw what ?

Answer 8

cos x + sin x = 0
cos x = -sinx

Answer 9

k then ?

Answer 10

why u delete that?

Answer 11

find the value of x

Answer 12

x=-pi/4 isnt it?

Answer 13

no we have to take the value from 0 to 2

Answer 14

then hw ??

Answer 15

take x = 135 degrees

Answer 16

convert it to radians

Answer 17

2.355

Answer 18

x=3pi/4

Answer 19

if x is between 0 to 2pi, then x= 3pi/4 is correct.

Answer 20

k then hw we find local maxima and local minima ?

Answer 21

local only means 'in that interval' , here 0 to 2pi

Answer 22

so what are maxima and minima here ?

Answer 23

so here u'll have only one value , at x=3pi/4
find f(x) when x=3pi/4

Answer 24

also at x=7pi/4 we have only one value so
f'(X)= ives 2 values for x isnt it?

Answer 25

f'(X)=0 gives 2 values for x isnt it?

Answer 26

oh yes! i missed that.
now its even simpler..... find the second derivate, what u get ?

Answer 27

-sinx +cos x

Answer 28

whats the use of taking second derivative ?

Answer 29

to know which point is max. or min. , u know how ?

Answer 30

nop

Answer 31

is it by substituting 3pi/4 and 7pi/4 in f''(X) and getting the sign to tell which is maxima and minima?

Answer 32

k gt it !!!

Answer 33

yes, if f''(x) > 0 , then max or min ?

Answer 34

ok, good :)

Answer 35

3pi/4 is max other is minima !!

Answer 36

can u check up the answer for the next qn also ?

Answer 37

sure ...

Answer 38

i will post separately