Answer:
Step-by-step explanation:
a) 2sf = 0.086
3sf = 0.0861
b) 2sf = 19
3sf = 19.3
81
(9x - 4)(9x + 4) = ax² - b
81x² - 36x + 36x - 16
= 81x² - 16
=> a = 81
See the attachment
Hope this helps :)
