In ABC M is the midpoint of AB and N divides CB such that NB:CB = 1:5 If the area of CAM is 30in find the area of MNB and ABC

Respuesta :

The ratio of the base of the triangles ΔMNB and ΔCBM, that

shares a common vertex, is the ratio of their areas.

Correct response:

  • Area of ΔMNB is 6 in.²
  • Area of ΔABC is 60 in.²

Which is the method used to find the area of the triangles

Given;

M is the midpoint of side AB in ΔABC

NB:CB = 1:5

Area of ΔCAM = 30 in.²

Required:

The area of ΔMNB and ΔABC

Solution:

[tex]Area \ of \ a \ triangle = \mathbf{\dfrac{1}{2} \times Base \times Height}[/tex]

Height of ΔCAM = Height of ΔCBM = Altitude of point C above line AB

MA = MB by definition of midpoint

MA is the base of ΔCAM, and MB is the base of ΔCBM

Therefore;

[tex]Area \ of \ \Delta CAM= \dfrac{1}{2} \times AM \times Height \ of \ \Delta CAM = \mathbf{\dfrac{1}{2} \times MB \times Height \ of \ \Delta CAM}[/tex]

Which gives;

Area of ΔCAM = Area of ΔCBM = 30 in.²

Area of ΔABC = Area of ΔCAM + Area of ΔCBM = 30 + 30 = 60

  • Area of ΔABC = 60 in.²

Taking CB as the base of ΔCBM, we have;

Height of ΔMNB = Height of ΔCBM from line CB

Base length of ΔCBM = 5 × Base length of ΔMNB

Therefore;

Area of ΔCBM = 30 in.² = 5 × The area of ΔMNB

[tex]Area \ of \ \Delta MNB = \dfrac{30 \ in.^2}{5} = \mathbf{ 6 \ in.^2}[/tex]

  • Area of ΔMNB = 6 in.²

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