हिंदी

In the adjacent figure, □ABCD is a trapezium AB || DC. Points M and N are midpoints of diagonal AC and DB respectively then prove that MN || AB.

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प्रश्न

In the adjacent figure, `square`ABCD is a trapezium AB || DC. Points M and N are midpoints of diagonal AC and DB respectively then prove that MN || AB.

योग
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उत्तर

Given: `square`ABCD is a trapezium. AB || DC

Points M and N are the midpoints of diagonals AC and DB respectively.  

To prove: MN || AB

Construction: Draw line DM which intersects side AB at point T.

Proof:

side DC || side AB      …(Given)

And seg AC is a transversal line.

∴ ∠DAC ≅ ∠BAC       ...(alternate angles)

∴ ∠DCM ≅ ∠TAM      ...(i)   ...(A-M-C and A-T-B)

In ∆DCM and ∆TAM,

∠DCM ≅ ∠TAM        ...[From (i)]

seg MC ≅ seg MA       ...(Point M is the midpoint of seg AC.)

∠DCM ≅ ∠TAM      ...(Vertically opposite angles)

∴ ∆DCM ≅ ∆TAM      ...(ASA test)

seg DM ≅ seg MT       ...(c.s.c.t)  ...(ii)

In ∆DTB,

Point N is the midpoint of line DB.     ...(Given)

Point M is the midpoint of line DT.     ...[From (ii)]

∴ seg MN || side TB    ...(Midpoint Theorem)

∴ seg MN || seg AB   ...(A-T-B)

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अध्याय 5: Quadrilaterals - Problem Set 5 [पृष्ठ ७४]

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बालभारती Mathematics 2 [English] Standard 9 Maharashtra State Board
अध्याय 5 Quadrilaterals
Problem Set 5 | Q 9 | पृष्ठ ७४

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