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CBSE Class 9 Answered

If a2 + b2 + c2 = 90 and a + b + c = 20 then find the value of ab + bc + ca.
Asked by Topperlearning User | 04 Jun, 2014, 01:23: PM
answered-by-expert Expert Answer

(a + b + c)2 = a2 + b2 + c2 + 2ab + 2bc + 2ca

(a+ b + c)2 = a2 + b2 + c2+ 2 (ab + bc + ca)

(20)2 = 90 + 2 (ab + bc + ca)

400 - 90 = 2 (ab + bc + ca)

ab + bc + ca = 155

Answered by | 04 Jun, 2014, 03:23: PM
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