-a − [a + {a + b − 2a − (a − 2b)} − b]
We will first remove the innermost grouping symbol ( ), followed by { } and then [ ].
∴ −a − [a + {a + b − 2a − (a − 2b)} − b]
= −a − [a + {a + b − 2a − a + 2b} − b]
= −a − [a + {3b − 2a } − b]
= −a − [a + 3b − 2a − b]
= −a − [2b − a ]
= −a − 2b + a
= −2b