Write a coordinate proof to prove that the segment that joins the vertex angle of an isosceles triangle to the midpoint of its base is perpendicular to the base .

Given: An Isosceles Triangle ABC with a vertex at B.

Midpoint M of the base AC.

To Prove: BM is perpendicular to AC.  

Proof:

Let the coordinates of the points of the isosceles triangle be given as:

A =  (-k, 0)

Vertex, B =  (0,a)  

C = (k, 0)

Midpoint, M = (0,0)

Slope of the base segment, AC:

Slope of the base segment,  AC=

Slope of the segment that joins the vertex angle of an isosceles triangle to the midpoint of its base, BM.

 = Undefined

Two lines are perpendicular if the gradient of one is a negative reciprocal of the other.

Since is a negative reciprocal of 0 for arbitrary values of a, BM and AC are perpendicular.

This concludes the proof.

answer for #1 is c

answer for #2 is d

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5x + 3y = - 4

step-by-step explanation:

the equation of a line in standard form is

ax + by = c ( a is a positive integer and b, c are integers )

express the line first of all in slope- intercept form

y = mx + c ( m is the slope and c the y-intercept )

to calculate m use the gradient formula

m = ( y₂ - y₁ ) / ( x₂ - x₁ )

with (x₁, y₁ ) = (7, - 3) and (x₂, y₂ ) = (4, - 8)

m = = -

y = - x + c ← is the partial equation

to find c substitute either of the 2 points into the partial equation

using (4, - 8 ), then

- 8 = - + c ⇒ c = -

y = - x - ← in slope-intercept form

multiply all terms by 3 to eliminate the fractions

3y = - 5x - 4 ( add 5x to both sides )

5x + 3y = - 4 ← in standard form