a and b are any natural numbers, and after k is a fixed number, if a△b=ab+k(a+b), and l△1=5, what is the value of 5△8?
a、b是任意自然数，k后是固定不变的数，规定a△b=ab+k(a+b)，且l△1=5，则5△8的值等于多少．
<gadget id="calculator">5 + 8</gadget>
<output>13</output>

<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">13 * 2</gadget>
<output>26</output>

<gadget id="calculator">40 + 26</gadget>
<output>66</output>

<result>66</result>