Co - Ordinate Geometry

abhi332 wrote:

Topic: Co - Ordinate Geometry
Sun Feb 07, 2010 1:15 am
if point (m,n) is a point on line with equation y=f(x) . which if the following must be point on line with equation y= -f(x)?

A . (m,n)
B. (m,-n)
C. (-m,n)
D. (-m-n)
E. cannot be determined

PLEASE HELP!!! Explain your reasoning!!

Since (m,n) is a point of y=f(x) .. so n=f(m).
now multiplying both sides by -1, we get -n=-f(m) .......(i)

now we have to find the point which lies on y=-f(x) ------(ii)
so from (i) and (ii) we get y=-n and x=m
Hence point lying on y=-f(x) is (m,-n)
The answer is B

abhi332 wrote:if point (m,n) is a point on line with equation y=f(x) . which if the following must be point on line with equation y= -f(x)?

A . (m,n)
B. (m,-n)
C. (-m,n)
D. (-m-n)
E. cannot be determined

PLEASE HELP!!! Explain your reasoning!!


OA B

Equation of a line in generic form is y = kx+c (k is the slope and c is the y intercept)

m,n is a point on y=kx+c so, n = mk+c
-f(x) => y = -kx -c
(m, -n) will satisfy this since substituting this value in the line we get n = mk+c

ajith wrote:

abhi332 wrote:if point (m,n) is a point on line with equation y=f(x) . which if the following must be point on line with equation y= -f(x)?

A . (m,n)
B. (m,-n)
C. (-m,n)
D. (-m-n)
E. cannot be determined

PLEASE HELP!!! Explain your reasoning!!


OA B

Equation of a line in generic form is y = kx+c (k is the slope and c is the y intercept)

m,n is a point on y=kx+c so, n = mk+c
-f(x) => y = -kx -c
(m, -n) will satisfy this since substituting this value in the line we get n = mk+c

Ajith I think this problem could be solved by just putting coordinates in function. Also the question says y=f(x) is the equation of a line and not a straight line. so you can't take in general an equation of straight line.

But you can use it as a plug-in method. Though I think for this question just coordinates will do.

shashank.ism wrote:
Ajith I think this problem could be solved by just putting coordinates in function. Also the question says y=f(x) is the equation of a line and not a straight line. so you can't take in general an equation of straight line.

But you can use it as a plug-in method. Though I think for this question just coordinates will do.

Well, I agree

Having said that, A curved line is generally called a curve and st. line is generally called a line. But, I agree that it cannot be taken for granted.