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Question
In fig. BD = 8, BC = 12, B-D-C, then `"A(ΔABC)"/"A(ΔABD)"` = ?
Options
2 : 3
3 : 2
5 : 3
3 : 4
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Solution
3: 2
In ΔABC and ΔABD,
ΔABC and ΔABD have the same height. ...(Given)
The ratio of the areas of two triangles with equal heights is equal to the ratio of their corresponding bases.
∴ `"A(ΔABC)"/"A(ΔABD)" = "BC"/"BD"`
∴ `"A(ΔABC)"/"A(ΔABD)" = 12/8`
∴ `"A(ΔABC)"/"A(ΔABD)" = 3/2`.
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(i) `"A(ΔABD)"/"A(ΔADC)"`
(ii) `"A(ΔABD)"/"A(ΔABC)"`
(iii) `"A(ΔADC)"/"A(ΔABC)"`
Prove that, The areas of two triangles with the same height are in proportion to their corresponding bases. To prove this theorem start as follows:
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In the figure, PQ ⊥ BC, AD ⊥ BC. To find the ratio of A(ΔPQB) and A(ΔPBC), complete the following activity.

Given: PQ ⊥ BC, AD ⊥ BC
Now, A(ΔPQB) = `1/2 xx square xx square`
A(ΔPBC) = `1/2 xx square xx square`
Therefore,
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= `square/square`
