Explanation:

 Step 1: Look up each octal digit to obtain the equivalent group of four binary digits. You can use the table below to make these conversions.

(5)₁₆ = (0101)₂
(A)₁₆ = (1010)₂

Step 2: Group each value of step 1
0101 1010

Step 3: Join these values and remove zeros at left (if necessary) to get the binary result.

1011010

So, 1011010 is the binary equivalent of hexadecimal number 5A