Answer:
[tex] {a}^{2}-4a - 21 = 0[/tex]
Step-by-step explanation:
[tex]4 - 4a - (5 + a)( 5- a) = 0[/tex]
[tex]4 - 4a - (25 - 5a + 5a - {a}^{2} = 0 [/tex]
[tex]4 - 4a - 25 + 5a - 5a + {a}^{2} = 0[/tex]
[tex] {a}^{2} - 4a + 5a - 5a + 4 - 25 = 0[/tex]
[tex] {a}^{2} - 4a - 21 = 0[/tex]
