ln a △ABC, A=30°+C and R=(3+1)r, where r is the inradius and R is the circumradius, then

(B) ABC is an equilateral triangle

(D) ∠A=75°, ∠B=60°, ∠C=45°

AP EAMCET · Maths · Properties of Triangles

ln a $△ A B C$ , $A = 30 ° + C$ and $R = (\sqrt{3} + 1) r$ , where $r$ is the inradius and $R$ is the circumradius, then

A $A B C$ is a right-angled triangle
B $A B C$ is an equilateral triangle
C $A B C$ is acute angled
D $∠ A = 75 °, ∠ B = 60 °, ∠ C = 45 °$

Verified Solution

Answer & Solution

Correct Answer

(A) $A B C$ is a right-angled triangle

Step-by-step Solution

Detailed explanation

Using r=4RsinA2·sinB2·sinC2 ⇒R3+1=4RsinA2·sinB2·sinC2 ∵R=3+1r ⇒3-18=sinA2·sinB2·sinC2 ⇒sinA2·sinB2·sinC2=3-122·12·12 Now, A2, B2, C2 are 12, 12, 3-122 and it is given that A=30°+C…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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