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If a+b+c=12, a^2+b^2+c^2=70, ab+bc+ca=37, find a,b,c. |
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Answer» Given : a² + b² + c² = 70, a + b + c = 12, ab + bc + ca = 37 To find : a, b and c Solution: (a + b + c)² = a² + b² + c² + 2(ab + bc + ca) => 12² = 70 + 2(37) => 144 = 70 + 74 => 144 = 144 Hence 3rd Equation can be found if 2 Equations are given Hence these 3 Equations are basically 2 Equations and 3 Variable a , b & c We can not solve 3 variables with 2 Equations There can be many possible solutions few are below : a = √37 i b = -√37 i c = 12 ( a , b & c can VARY ) Verification a² + b² + c² = -37 - 37 + 144 = 70 (i² = -1) a + b + c = √37 i -√37 i + 12 = 12 ab + bc + ca = (√37 i) * (-√37 i) + (√37 i) 12 + (-√37 i) 12 = 37 Not ENOUGH Details to find Unique Solutions we can choose any one value then find others let say a = 0 => b + c = 12 bc = 37 => x² - 12x + 37 = 0 => b & c = ( 12 ± √144 - 4 * 37 ) / 2 = 6 ± i a = 0 , b = 6 + i , c = 6 - i a + b + c = 12 a² + b² + c² = 0 + 36 - 1 + 12I + 36 - 1 - 12i = 72 ab + bc + ca = (6 + i)(6 - i) = 36 - i² = 36 -(-1) = 37 Hence if we assume one value we can get others a = 1 => b + c = 11 & bc = 26 x² - 11x + 26 = 0 b & c = (11 ± √17)/2 a = 2 => b + c = 10 & bc = 17 x² - 10x + 17 = 0 b & c = (10 ± √32)/2 = 5 ± 2√2 and so on limit less solution Learn more: if x+y+z=0 then the SQUARE of the value of (x+y)^2/xy+(y+z)^2/yz+(z+x) Find x,y,z using cramers rule, if x-y+z=4, 2x+y-3z=0 and x+y+z=2 a+b+c=12, a^2+b^2+c^2=70, ab+bc+ca=37 find a,b,c |
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