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Need help with coordiantes and ratio

" F lies on a line AB such that AF is 3/4 of the length of AB. Given that 𝐴(0,0) and 𝐹(18,−9), find the point B. "

So I used the formula: X = M₁ x X₂ + M₂ x X₁/ M₁ + M₂
Y= M₁ x Y₂ + M₂ x Y₁/M₁ + M₂

I then subbed in the numbers to get:

X = 3 x 18 + 1 x 0/3 + 1
X = 13.5

Y = 3 x -9 + 1 x 0/3 + 1
Y = -6.75

(13.5, -6.75)

However I wrote this off as the X coordinate of point F (18) is bigger than the X coordinate of point B (13.5). Is this correct? If not, where did I go wrong and what's the best way to find the coordinates of point B?

(edited 4 years ago)

Reply 1

T!gger34

Original post by Soul Wavel3ngth

Yep, both your X and Y are incorrect.
A simpler way is to consider that for X, the horizontal distance from A (18) to F is 3/4 of the distance to B. So, what's the distance from A to B?
Similar for Y.