Question

You says on the picture

Answer 1

Pythagoras Theorem:

$\boxed {\boxed {a^2 + b^2 = c^2}}$

Apply Pythagoras Theorem:
$5.2^2 + b^2 = 7^2$

Take away 5.2² from both sides:
$b^2 = 7^2 - 5.2^2$

Evaluate the Right Hand Side:
$b^2 = 21.96$

Square root both sides:
$b = \sqrt{21.96}$

Evaluate the Right Hand Side:
$b = 4.7$

$\boxed{\boxed{\text{Answer = 4.7 mm}}}$

Answer 2

Use the Pythagorean Theorem. a^2+ b^2=c^2.
In this case, it is c^2-b^2=a^2, so your answer is 4.686 mm^2. Round if you need to.