ICSE 9 Maths
Isosceles Triangles
Question 1:
In an isosceles triangle ABC, with AB = AC, the bisectors of ∠ B and ∠ C
intersect each other at O. Join A to O. Show that:
(1) OB = OC
(2) AO bisects ∠ A
Question 2:
In Δ ABC, AD is the perpendicular bisector of BC (see fig). Show that Δ ABC is an isosceles triangle in which AB = AC.
Question 3:
ABC is an isosceles triangle in which altitudes BE and CF are drawn to equal
sides AC and AB respectively (see fig). Show that these altitudes are
equal.
Question 4:
ABC is a triangle in which altitudes BE and CF to sides AC and AB are equal (see
fig). Show that
(1) Δ ABE ≅ Δ ACF
(2) AB = AC, i.e., ABC is an isosceles triangle.
Question 5:
ABC and DBC are two isosceles triangles on the same base BC (see Fig).
Show that ∠ ABD = ∠ ACD.
Question 6:
ΔABC is an isosceles triangle in which AB = AC. Side BA is produced to D such
that AD = AB (see Fig). Show that ∠ BCD is a right angle.
Question 7:
ABC is a right-angled triangle in which ∠ A = 90⁰ and AB = AC. Find ∠ B and ∠ C.
Question 8:
Show that the angles of an equilateral triangle are 60⁰ each.
Question 9:
Δ ABC and Δ DBC are two isosceles triangles on the same base BC and vertices
A and D are on the same side of BC (see Fig). If AD is extended to
intersect BC at P, show that
(1) Δ ABD ≅ Δ ACD
(2) Δ ABP ≅ Δ ACP
(3) AP bisects ∠ A as well as ∠ D.
(4) AP is the perpendicular bisector of BC.
Question 10:
AD is an altitude of an isosceles triangle ABC in which AB = AC. Show that
(1) AD bisects BC.
(2) AD bisects ∠ A.
Question 11:
BE and CF are two equal altitudes of a triangle ABC. Using RHS congruence
rule, prove that the triangle ABC is isosceles.
Question 12:
ABC is an isosceles triangle with AB = AC. Draw AP ⊥ BC to show that ∠ B = ∠ C.
Question 13:
In DABC, AB = AC and ÐB = 50°. Then, ÐC is equal to
(a) 40°
(b) 50°
(c) 80°
(d) 130°
Question 14:
In DABC, BC = AB and ÐB = 80°. Then, ÐA is equal to
(a) 80°
(b) 40°
(c) 50°
(d) 100°
Question 15:
In DPQR, ÐR = ÐP and QR = 4 cm and PR = 5 cm.
Then, the length of PQ is
(a) 4 cm
(b) 5 cm
(c) 2 cm
(d) 2.5 cm
Question 16:
In triangles ABC and PQR, AB = AC, ÐC = ÐP and ÐB = ÐQ. The two triangles are
(a) isosceles but not congruent.
(b) isosceles and congruent.
(c) congruent but not isosceles.
(d) neither congruent nor isosceles.
Question 17:
D is any point on side AC of a DABC with AB = AC. Show that CD < BD.
Question 18:
Bisectors of the angles B and C of an isosceles triangle with AB = AC intersect each other at O. BO is produced to a point M. Prove that ÐMOC = ÐABC.
Question 19:
In the given figure, AD is the bisector of ÐBAC. Prove that AB > BD.
Question 20:
Find all the angles of an equilateral triangle.
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All About Daily Practice Problems on ICSE 9 Maths Isosceles Triangles NCERT Chapter 10
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