w give me solution of this 3 questions question guys please help me
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its there in ncert solutions! !
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for the third probl: (see diagram).
Draw a circle with AC as the diameter (O is midpoint of AC). The circle will pass through B and D. Reason is that angle in a semicircle is a right angle.
Now the chord (or arc) CD makes equal angles on the circle, we know this. Hence, ∠CBD = ∠CAD.
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probl 2: see diagram.
Circles on two sides intersect on the third.
Let ABC be a triangle (let BC be along horizontal). Draw a circle with AB as the diameter intersecting AC at D. ∠BDA = 90° (angle in semicircle).
Draw a circle with BC as the diameter. Let it intersect AC at E and the first circle at F. Let O be the midpoint of AB and P be the midpoint of BC.
∠BEC = 90° as it is in a semicircle.
We know OP is the line joining midpoints. So it is parallel to AC.
Line BF is the common chord. We know it is perpendicular to line joining centers. So BF ⊥ OP, so BF ⊥ AC.
We see that BD ⊥ AC , BE ⊥ AC, BF ⊥ AC
Since B is common among all these above, D, E and F are the same point.
Hence the circles intersect on the third side.
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the first problem see diagram.
we use the principles of similar triangles.
ΔASC and ΔPSB are similar, as ∠CAB and ∠CPB are equal (angles in a segment made by chord/arc CB). ∠PSB = ∠ASC (vertical angles).
Hence, ∠PBS = ∠ACP. -- (1)
∠PBS = ∠DBT (vertical angles). -- -(2)
∠BDC = ∠BQC (angles in the same segment made by arc BC).
∠DTB = ∠CTQ.
So ΔDTB & ΔQTC are similar.
So angle ∠QCD = ∠DBT --- (3)
Hence, ∠ACP = ∠QCD by (1), (2) and (3).
Draw a circle with AC as the diameter (O is midpoint of AC). The circle will pass through B and D. Reason is that angle in a semicircle is a right angle.
Now the chord (or arc) CD makes equal angles on the circle, we know this. Hence, ∠CBD = ∠CAD.
=======
probl 2: see diagram.
Circles on two sides intersect on the third.
Let ABC be a triangle (let BC be along horizontal). Draw a circle with AB as the diameter intersecting AC at D. ∠BDA = 90° (angle in semicircle).
Draw a circle with BC as the diameter. Let it intersect AC at E and the first circle at F. Let O be the midpoint of AB and P be the midpoint of BC.
∠BEC = 90° as it is in a semicircle.
We know OP is the line joining midpoints. So it is parallel to AC.
Line BF is the common chord. We know it is perpendicular to line joining centers. So BF ⊥ OP, so BF ⊥ AC.
We see that BD ⊥ AC , BE ⊥ AC, BF ⊥ AC
Since B is common among all these above, D, E and F are the same point.
Hence the circles intersect on the third side.
===================
the first problem see diagram.
we use the principles of similar triangles.
ΔASC and ΔPSB are similar, as ∠CAB and ∠CPB are equal (angles in a segment made by chord/arc CB). ∠PSB = ∠ASC (vertical angles).
Hence, ∠PBS = ∠ACP. -- (1)
∠PBS = ∠DBT (vertical angles). -- -(2)
∠BDC = ∠BQC (angles in the same segment made by arc BC).
∠DTB = ∠CTQ.
So ΔDTB & ΔQTC are similar.
So angle ∠QCD = ∠DBT --- (3)
Hence, ∠ACP = ∠QCD by (1), (2) and (3).
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