Two equal circles pass through each other’s centre. If the radius of each circle is 5 cm, what is the length of the common chord?
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Answers
GIVEN: 2 equal circles with centre A & radii AP, AB, AQ = 5 cm And circle with centre B, & radii BP, BA & BQ = 5 cm. PQ is a common chord to both the circles.
TO FIND: PQ= ?
Since APBQ is a rhombus, as all its sides = 5 cm & one diagonal AB = 5 cm
So, triangle PAB & triangle QAB are equilateral triangles ( as all 3 sides are equal in each triangle)
Area of equilateral triangle = (√3/4) side²
=> area of triangle PAB = (√3/4)* 25 cm²
=> area of both triangles = 2* ( √3/4) *25
=> (25√3 /2 ) cm² = area of rhombus PAQB …(1)
NOW, area of rhombus = 1/2 * diagonal AB * diagonal PQ
=> 1/2 * 5 * PQ = 25√3 /2…. ( by (1) )
PQ = (25√3/2) * (2/5)
=> PQ = 5√3 cm …
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ɢɪᴠᴇɴ :- equal circles with centre A & radii AP, AB, AQ = 5 cm And circle with centre B, & radii BP, BA & BQ = 5 cm. PQ is a common chord to both the circles.
ᴛᴏ ꜰɪɴᴅ : ᴘQ= ?
Sɪɴᴄᴇ , APBQ is a rhombus, as all its sides = 5 cm & one diagonal AB = 5 cm
ꜱᴏ , triangle PAB & triangle QAB are equilateral triangles ( as all 3 sides are equal in each triangle)
ᴀʀᴇᴀ ᴏꜰ ᴇQᴜᴀɪʟᴀᴛᴇʀᴀʟ ᴛʀɪᴀɴɢʟᴇ = (√3/4) side²
⇨ ᴀʀᴇᴀ ᴏꜰ ᴛʀɪᴀɴɢʟᴇ ᴘᴀʙ = (√3/4) × 25 cm²
⇨ ᴀʀᴇᴀ ᴏꜰ ʙᴏᴛʜ ᴛʀᴀɪɴɢʟᴇ = 2 ×( √3/4) × 25
⇨(25√3 /2 ) cm² = ᴀʀᴇᴀ ᴏꜰ ʀʜᴏᴍʙᴜꜱ ᴘᴀQʙ …(1)
ɴᴏᴡ , ᴀʀᴇᴀ ᴏꜰ ʀhombus = 1/2 × ᴅiagonal AB ×
ᴅiagonal PQ
⇨ 1/2 × 5 × PQ = 25√3 /2…. ( by (1) )
PQ = (25√3/2) × (2/5)
⇨PQ = 5√3 cm
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