If `a+b+c = 5 and a^2+b^2+c^2 = 13`; find `ab+bc+ac`

If a + b + c = 13, a^2 + b^2 + c^2 = 69, " then find " ab + bc + ca .

Let Delta = |(-bc, b^2 + bc, c^2 + bc),(a^2 + ac , - ac, c^2 + ac),(a^2 + ab , b^2 + ab, -ab)| and the equation px^3 + qx^2 + rx + s = 0 has roots a,b,c where a,b,c in R^(+) , then if Delta = 27 and a^2 + b^2 + c^2 = 2 , find (sqrt(2) p)/(q) + 1 .

If a+b+c=13,a^(2)+b^(2)+c^(2)=69, then find ab+bc+ca.-50 (b) 50 (c) 69 (d) 75

If a+b+c=4 and a^(2)+b^(2)+c^(2)+3(ab+bc+ac)=21 where a, b, c in R then ab+bc+ca=

If a:b = 4:5 and b:c = 2:3, then a:c=_____.

If a:b=4:5 and b:c=2:3, then a:c=