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urgent math help needed (lines)

The points A (3,5) and B (5,-8) lie on the line L1.
a) Find the gradient of L1
= i already did this, -13/2

A second line, L2, is perpendicular to L1.
b) Write down the gradient of L2
= 2/13

L2 passes through points P (5,0) and Q (t,2)
c) find the value of t.
= I DONT KNOW!!! can someone explain step by step how to get to the ans. thanks
Original post by whatfuture
The points A (3,5) and B (5,-8) lie on the line L1.
a) Find the gradient of L1
= i already did this, -13/2

A second line, L2, is perpendicular to L1.
b) Write down the gradient of L2
= 2/13

L2 passes through points P (5,0) and Q (t,2)
c) find the value of t.
= I DONT KNOW!!! can someone explain step by step how to get to the ans. thanks


Gradient = Change in y / Change in x.

Work out the change in y, then use that to get the change in x.
Do you know the gradient of l2?
What can you do with that value?
Original post by whatfuture
The points A (3,5) and B (5,-8) lie on the line L1.
a) Find the gradient of L1
= i already did this, -13/2

A second line, L2, is perpendicular to L1.
b) Write down the gradient of L2
= 2/13

L2 passes through points P (5,0) and Q (t,2)
c) find the value of t.
= I DONT KNOW!!! can someone explain step by step how to get to the ans. thanks


You're given that the gradient of L2L_2 is 213\frac{2}{13}, and that it passes through the point (5,0)(5,0). How can we use this information to derive an equation for L2L_2, and hence work out the value of tt? Recall that you can express the equation of a linear line as y=mx+cy=mx+c, where mm is the gradient.
Original post by TimGB
Gradient = Change in y / Change in x.

Work out the change in y, then use that to get the change in x.


The OP already has the gradient of L2L_2 :smile:
213=20t5\dfrac{2}{13} = \dfrac{2-0}{t-5}
Original post by _gcx
The OP already has the gradient of L2L_2 :smile:


I know, I'm helping them with part c). OP just needs to use the same formula as part a).
(edited 6 years ago)
Original post by TimGB
I know, I'm helping them with part c). OP just needs to use the same formula as part a).


Ah, my mistake :smile:

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