Answer:
(5x+2)(x-2)
Step-by-step explanation:                      
-       5x^2-8x-4
 -       5x^2-10x+2x-4
 -       (5x^2-10x)+(2x-4)
 -        5x(x-2) +2(x-2)
 -       (5x+2)(x-2)           ✔️
 
                                                           
If you want to learn how I did this its below this message but its very complicated to write it out so I suggest watching a khan academy video or something.
                                                             Note: First Term is <u>5x^2</u>
                                                             Middle Term is <u>-8x</u> and Last Term is <u>-4</u>
                                                            Coefficient- The number in front of x
<h3>Step 1:   Write out problem
          </h3><h3 />
 5x^2-8x-4                              
<h3>Step 2: Using Diamond/Grouping method </h3>
             
Multiply first term coefficient and last term's coefficient
to get a number.                                                 5×-4    = -20    
Now find 2 numbers that can multiply into this number   ↑ and those 2 numbers also have to add up to the middle term (-8).
So basically find 2 numbers that multiply to -20 and add up to -8.    In this case those numbers are gonna be -10 and 2 because -10×2=-20 and -10+2=-8
<h3>Step 3: Split the Middle Term</h3>
Okay now rewrite the problem out           5x^2-8x-4
Now  rewrite it again but replace the -8x with the 2 numbers you got and add an x after the numbers.                    5x^2-10x+2x-4
Now split the problem into 2 parts:         (5x^2-10x)    +    (2x-4) 
Now factor out the highest GCF out of the first section of the problem.  For this problem factor out 5x out of (5x^2-10x)
You now have 5x(x-2)    +   (2x-4)
Now factor out the next part of the problem which is 2 in this problem
Now you have this      <u>5x</u> (x-2)    +   <u>2</u> (x-2)
Now you take this        ↑   and this  ↑   and stick them inside a parenthesis.
You now have (5x+2)        to finish it off just take (x-2) and put it next to (5x+2)
Answer:   (5x+2)(x-2)
Congrats you probably didn't understand. Sorry for wasting your time if you didn't understand.
                                                                                  
<h2 />