7 pillars are used to hold a slant rod as shown in the figure. If the distance between every two pillars is 1 m and first pillar is 1 m from the rod leg. Height of the last pillar is 10.5 m. Find the height of first pillar.
A
1.5
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B
2.5
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C
3.5
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D
0.5
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Solution
The correct option is A 1.5 Let
PQ be the first pillar, AB be the last pillar and AC be the slant rod. x is the height of the first pillar to be found.
From the given figure, AP and QB are transversals for parallel lines PQ and AB. ∠P=∠A [Corresponding angles are equal] ∠Q=∠B [Corresponding angles are equal]
and ∠C is common angle for both triangles.
Since, three corresponding angles for two triangles are equal. ΔABCandΔPQC are similar, so their sides will be proportional. ⇒PQAB=CQCB⇒x10.5=11+6⇒x=10.57x=1.5m