# arrow_back Then the value of $a b+b c+c a$ is

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If $a^{2}+b^{2}+a b=11^{2}$
$b^{2}+c^{2}+b c=13^{2}$
$c^{2}+a^{2}+c a=20^{2}$
where $a, b, c \in \mathbb{R}^{+}$
Then the value of
$a b+b c+c a$
is
a. 150
b. $88 \sqrt{3}$
c. $66 \sqrt{5}$
d. 120

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