Saturday, March 17, 2012

The vertices of trianglePQR are P(1,3), Q(5,4) & R(5,15). Find the length of PR, area of TrianglePQR & length of per. line drown fm Q to PR.

To find the length of PR, we'll use the distance
formula:


PR= sqrt[(xR-xP)^2 +
(yR-yP)^2]


PR =
sqrt[(5-1)^2+(15-3)^2]


PR =
sqrt(16+144)


PR = sqrt 160


PR
= sqrt 16*10


PR = 4*sqrt
10


 Let's calculate the length of the segment
QP


QP =
SQRT[(xP-xQ)^2+(yP-yQ)^2]


QP =
sqrt[(1-5)^2+(3-4)^2]


QP =
sqrt(16+1)


QP = sqrt 17


Now,
let's calculate QR


QR = sqrt
[(5-5)^2+(15-4)^2]


QR = sqrt
11^2


QR = 11


Area of the
triangle will be calculated with Heron formula:


A =
sqrt[p(p-QP)(p-QR)(p-PR)]


where p =
(QR+QP+PR)/2


To calculate the height QM, we'll have to find
out the equation of PR , using the standard form y = mx+n, where m is the slope of PR.
After that, we'll consider the constraint the 2 lines are perpendicular if and only if
the product of  their slopes is -1.


To find the equation of
PR, we'll consider the formula:


(xR-xP)/(x-xP) =
(yR-yP)/(y-yP)


(5-1)/(x-1) =
(15-3)/(y-3)


4/(x-1) =
12/(y-3)


We'll divide by 4 both
sides:


1/(x-1) = 3/(y-3)


We'll
cross multiply:


3x-3 =
y-3


We'll add 3 both sides:


3x
= y


So the slope of PR is m1 =
3


The slope of QM is m2 =
-1/3.


The equation of QM is:


y
- yQ = (-1/3)(x-xQ)


y-4 =
(-1/3)(x-5)

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